Heat Sterility in Meat Rabbits (Preparing For, and Managing)

With the onset of summer comes the potential for meat rabbits to become sterile. This is something that can happen in periods of very high heat, worsened by high humidity.

Fortunately, in and of itself, heat sterility is not a critical condition. But it is one to be aware of and one worth knowing about, so that you can consider its potential to impact your rabbitry and breeding program.

Jump to:

• What is Meat Rabbit Heat Sterility?
• Who is Affected?
• Will Meat Rabbit Bucks Attempt to Breed If They Are Heat Sterile?
• How Hot is Too Hot?
• What Steps Can You Take to Avoid Heat Sterility in Meat Rabbits?
• VIDEO: Heat Sterility in Meat Rabbits: What is It? And How Can You Manage It?
• Rebounding from Heat Sterility and Being Able to Breed Again
• Ways to Minimize the Effects and Impacts of Meat Rabbit Heat Sterilization
• Keep Possible Heat Sterility in Mind When Making Culling, Retirement, and Selection Decisions
• How Serious a Problem is Heat Sterility for Meat Rabbits?

What is Meat Rabbit Heat Sterility?

Heat sterility is when a meat rabbit buck becomes temporarily sterile as a result of high heat killing sperm. When summer heat remains high for an extended number of consecutive days, bucks often become sterile for a time.

Who is Affected?

You might have guessed by now, but heat sterility is a problem for meat rabbit bucks.

Though does can be less willing to breed if they are being stressed by heat, and heat prostration can stress them to where their fertility might be somewhat impacted, their eggs generally remain viable if they do meet with sperm, and fertilization will occur if the sperm is potent (barring other reproductive issues).

Older bucks are usually affected more by high heat in general, and they are also more likely to become heat sterile. Older bucks are also more likely to remain sterile for longer than younger bucks.

However, if the heat is high, most bucks will succumb to heat sterility, at least for a period of time, regardless of their age.

Will Meat Rabbit Bucks Attempt to Breed If They Are Heat Sterile?

As long as they are not feeling too physically taxed or stressed from the heat, then yes, bucks, even if sterile, will attempt to mount and breed does.

So, you may see the act being done, and fall offs may occur, but your does may still not get bred during the hot months of the year (and for a time after -- see below).

If you are breeding or trying to breed meat rabbits in the warm months, you should plan matings for the coolest times of the day -- generally, early in the morning. This is to avoid overexertion and heat stroke in either animal (doe or buck).

How Hot is Too Hot?

The conditions that tend to result in bucks becoming sterile are a combination of time and temperature.

A single hot day is not usually enough to make a buck sterile. So if you have the odd high heat day, you will still be fine. But if high heat continues, heat sterility becomes quite likely.

There are two general parameters given for what makes a meat rabbit buck go sterile. For practical purposes, consider that either/or, or something close to both, may potentially cause sterility for your meat rabbit bucks.

The time and temperatures that we expect meat rabbit bucks to go sterile are:

• 5 or more days of temperatures that exceed 85℉ (29.4℃)
• 3 consecutive days of temperatures over 90℉ (32.2℃)

Of course, this isn’t set in stone and there are variables and exceptions, too.

For example, if temperatures cool significantly at night and the bucks get some respite from the heat, they may not become sterile. Or, they may be less potent, but not entirely sterile. You may see smaller litters in that case.

If housing conditions afford some relief from the high heat, then the bucks may not be impacted, or may only be moderately impacted.

Not all breeds and not all bucks are the same, either. Some handle heat better than others. Some will not go sterile in high heat, or not always.

And again, age can be a factor.

What Steps Can You Take to Avoid Heat Sterility in Meat Rabbits?

Truth be told, you may or may not be able to avoid heat sterility in your rabbitry. A lot depends on where you live and the typical conditions there. A lot depends on the heat from one summer to the next.

Unless you can control the weather, there is only so much you can do.

But you can set yourself and your rabbits up for the highest likelihood of avoidance, success, and rebounding from periods of heat sterility. Here are some ways to do that.

Selectively breed for your climate

Rabbits can handle and respond to stressors like heat differently. Overall, you won’t see a world of difference among meat rabbit breeds. As larger breeds, meat rabbits do tend to be more susceptible to heat sterility than smaller breeds do, but even small breeds and pet breeds can go heat sterile.

That said, if you see that a certain buck or line of bucks remains potent when others are not producing after high heat, then selecting toward that trait would be wise.

You should also be selecting towards rabbits that handle the heat well, even when you’re not expecting them to perform, and toward rabbits that navigate your seasons and different temperatures well all year round.

That may seem like a tall order, and it will take time, but suffice it to say that if you select for the conditions that your rabbits will experience, you’ll build stronger stock over time. And that stock may achieve a level of resistance to heat sterility.

Cages, cage, and housing placement

When you set up your rabbitry, keep future heat in mind.

If you are housing your rabbits in a shed or a barn, make sure that there is adequate ventilation and very good air flow. This is important all year long, but it can be critical in the summer to keep things cool.

Your rabbitry, whether inside or out, should be set up in a space that gets well shaded in the summertime. In summer, rabbits can’t handle direct sunlight. They don’t even like it very much in the winter.

Avoid overcrowding in cages. Bucks should be housed alone anyway, unless you are doing a colony system (and even then, many people choose to house bucks separately until they want them to breed their does). If you are using some sort of group housing situation, make sure there is plenty of space for rabbits to get away from each other.

This may also mean watching how closely spaced or blocked off your cages are from good air flow.

Find the coolest spot in your rabbitry, and house your breeding bucks there.

For those housing meat rabbits in cages or tractors, wire is best. It provides protection and ample air flow, and does not heat up from the rabbit’s body heat in enclosed spaces (this can be a problem in some hutches).

Wire cage bottoms are especially important because meat rabbits will stretch out to rest and cool off. Open wire allows for more cooling and keeps rabbits from getting too hot on solid cage floors.

Comfort measures

You can attempt some comfort measures to help your rabbits through the worst of the heat. Many meat rabbit raisers employ these methods. They can be difficult to manage continuously, though. And some say they see varying results.

Eric and Callene Rapp (authors of Raising Rabbits for Meat) say that they find many of these methods to be just too difficult to employ on a large scale, and they focus more on efforts relating to housing and management, such as those listed above. Changing out frozen water bottles several times a day, for example, or even having enough freezer space to constantly freeze them, can prove nearly impossible.

Some common comfort measures rabbit breeders employ include:

• Ice bottles (frozen bottles of ice for the rabbits to lay against or to release cooling air as wind or fans blow over them)
• Cold tiles -- stone floor tiles that are cooled in the fridge or freezer and exchanged
• Cooling fans for airflow (most effective if they can move cooler air in or around the rabbit area, less effective if they are just moving the same warm air)
• Misters*
• Misting ears with a spray bottle to increase heat exchange*
• Climate control (AC)*
• Reduce handling
• Avoid “extra” handling and maintenance such as breeding, nail trimming, etc.

*Take care that misters or spraying ears with water does not create a new problem, like skin issues, fly strike, or increasing humidity in the rabbitry, which can make high heat temperatures even worse for your rabbits.

**Some breeders do install air conditioning in their rabbit barns. As my goals are more sustainable, tolerant animals, and one of the benefits of raising rabbits is minimal utility inputs, I’m not a fan. You would also have to be careful with air conditioning to not create too sudden or too variable conditions.

**It is not wise to bring rabbits indoors to your home air conditioning if they are not used to it. The variation and shock of the difference alone could cause more problems than it solves. Constantly moving rabbits in and out of their home space is a stressor, too, and stacking stress is not going to help your rabbit deal with heat stress, especially if it stops them from eating or drinking. Better to set your rabbits up in the best location you can, and make heat tolerance a goal of your program.

You may find a happy medium. For example, you may provide ice bottles during the hottest part of the day, for the most critical hours. Or, you may provide them only for your bucks, or for bucks and breeding does, since they are the hardest to replace and are larger and more vulnerable to high heat. Or, you could provide them just for your bucks to stave off heat sterility.

Other than checking regularly that rabbits have enough water, leave them alone and don’t disturb them or break their rest and peace! Rabbits startle and jump easily. If they're calm and trying to rest and cool off, leave them to it unless it is to see to an essential need!

Regular breeding

Breeding on a steady and consistent basis is the best way to keep all meat rabbits in the highest of reproductive health.

The University of Michigan reports that bucks that breed frequently are less likely to become sterile from heat anyway: “Bucks that mate relatively often (about twice a week) are less likely to be affected by high temperatures than bucks that don’t mate as often.”

So, while your instinct may be to give your rabbits a break, breeding can actually be what keeps them from becoming heat sterile.

If you are breeding in hot weather, breed during the coolest part of the day (early morning). If temperatures have cooled to a fairly comfortable level and it won't tax the rabbits too much, it helps to do a second breeding later in the evening, when things have cooled off. If they look too stressed, better to wait until cooler temperatures prevail and/or skip the second round mating.

VIDEO: Heat Sterility in Meat Rabbits: What is It? And How Can You Manage It?

https://youtu.be/rwzdEPGg4ho

Rebounding from Heat Sterility and Being Able to Breed Again

Rebounding from heat sterility is simple. Get your bucks breeding again!

The best way to increase your bucks’ potency is to get them to clean out their systems and produce new sperm. The only way they will do that is by attempting breedings.

Heat sterility is temporary, and it shouldn’t last more than a couple of months.

• Young bucks should become potent again within 60 days of the last high heat period
• Older bucks may stay sterile up to 90 days, but they, too, should rebound if they’re not too old

So again, the answer is breeding.

Don’t be surprised if the first mating or two is unsuccessful or does not result in kits, even if you see the buck have fall offs.

Also, know that litters after sterile periods can be small. This is probably just from a lower sperm count as the buck comes back from its temporary infertility.

Ways to Minimize the Effects and Impacts of Meat Rabbit Heat Sterilization

Good management and planning will minimize the impacts that heat sterility has on your rabbitry as a whole. If you live in an area that is likely to experience one or more heat waves (usually considered 3 days or more over 90℉ or 32.2℃), then you need to factor heat sterility into your goals and breeding program.

Time Breedings According to Your Location and Climate

Even if you usually breed successfully throughout the summer, if you are relying on having kits at certain times, or a certain number of kits either for harvest or for sales, plan to breed early in the spring and summer to get kits on the ground before the high heat may stop your production for a while.

This may be a time of year when you want to breed more frequently or more intensively than you normally would during the rest of the year.

That said, if heat is moderated through living conditions or there is enough of a respite at night, or if you’ve bred and selected for resistance to heat sterility, it is entirely possible that you can breed all year round, even in a hot location.

Rotate and retire breeders to maintain the strongest, healthiest, most resistant, and resilient stock

As mentioned, younger bucks are less affected by heat sterility. They are also more resilient and more likely to rebound faster than older bucks.

In addition, age makes heat stress harder on breeders overall. Even if an old buck does not become sterile, he may be subject to too much stress from the heat. That is a situation that can become a downward spiral.

All of these are reasons to keep your bucks and breeders on the young side. It would be especially wise to replace an older breeding buck before summer if you sense that they are beginning to decline in productivity.

Keep Possible Heat Sterility in Mind When Making Culling, Retirement, and Selection Decisions

The potential for heat sterility is something that plays into the overall management of your meat rabbit breeding program.

When you are deciding who to breed and when, look at the calendar and consider the weather.

Consider your likely summer weather and how likely your bucks are to become sterile from high heat. And plan your breeding calendar and other important decisions like retirement and culling with that likelihood in mind.

You also need to consider whether you have had sterility-causing high heat before you cull or retire a good buck. If the conditions and timing are right, what seems like a failure of the buck may just be temporary heat sterility.

How Serious a Problem is Heat Sterility for Meat Rabbits?

In the grand scheme of things, heat sterility is not that much of a problem for meat rabbits. Which is not to say that it won’t happen; it’s just that it is a temporary condition, and the rabbit will bounce back and be able to breed again when temperatures moderate.

Heat sterility is something we, as rabbit breeders, need to be aware of, prepared for, and manage. Sterility itself, though, will come and go, and sterility will not be a problem for your meat rabbit bucks in terms of it being an overall health risk.